- Email: [email protected]
Low pressure, highly active rhodium catalyst for the homogeneous hydroformylation of olefins
Journal of Molecular
Catalysis, 34 (1986)
213 - 219
213
LOW PRESSURE, HIGHLY ACTIVE RHODIUM CATALYST FOR THE HOMOGENEOUS HYDROFORMYLATION OF OLEFINS A. M. TRZECIAK Institute
and J. J. ZI6LKOWSKI
of Chemistry,
(Received March 1,1985;
University
of Wrockaw, 50-383
Wrodhw
(Poland)
accepted June 21,1985)
Summary Hex-1-ene hydroformylation was examined at pressures of 1 - 11 atm and 40 “C, using Rh(acac)[P(OPh),], + P(OPh)s as catalyst. The highest efficiency of aldehydes was achieved employing a small P(OPhs), excess [P(OPh),]:[Rh] = 2:l. For reactions carried out at 1 atm, very high n/iso ratios i.e. lo-80 were obtained. Pressure increase caused a systematic drop of the n/iso ratio to ca. 5 at 11 atm. Simultaneously with hydroformylation, isomerisation of hex-lene to hex-2-ene occurs, but the contribution of the latter declines with increasing pressure. IR examination of the reaction mixture revealed that HRh(CO)[P(OPh)s]s was the active form of the catalyst. The same catalytic system was applied in propylene hydroformylation at 5 - 10 atm pressure and 40 “C. In such conditions the yield of aldehydes was 10 - 7096, with a n/iso selectivity of 2 - 10.
Introduction Rhodium(I) complexes containing a single ,&diketonate ligand of the type Rh@-diket.)LILz (where Li, LZ = CO, PPhs) have been recognized for many years as very convenient precursors for homogeneous catalysts of such reactions as hydrogenation, isomerisation and hydroformylation of olefins. In our recent papers on the catalytic reactivity of Rh(acac)[P(OPh),],, the hydrogenation of arenes [l] and hydroformylation [ 21 of olefins have been reported. This paper presents new results on the homogeneous hydroformylation of hex-1-ene and propylene. Experimental Rh(acac)Bis(triphenylphosphite)(acetylacetonato)rhodium(I), was obtained according to the method described earlier [3] P(OPhM,, (P(OPh), = P). IR spectra in benzene solution were recorded on a Specord 0304-5102/86/$3.50
0 Elsevier Sequoia/Printed in The Netherlands
214
75 IR instrument. The hex-l-ene hydroformylation products were analyzed by GLC and NMR methods (in Table 1 average results of both methods are given). GLC analysis: n- and iso-aldehydes were determined on a Chrom 4 instrument with cyclohexene as internal standard. NMR analysis: total amount of aldehydes, as well as amounts of hex-l-ene and hex-2-ene, were determined from the appropriate peak area on the ‘H NMR spectra. Dioxane was used as an internal standard. ‘H NMR spectra were recorded on a Tesla 80 MHz spectrometer. Propylene hydroformylation products were determined from ‘H NMR.
Results and discussion Hydroformylation of hex-l-ene Hex-1-ene hydroformylation was carried out under mild conditions, at 1 - 11 atm pressure and 40 “C. The composition of the reaction products is shown in Table 1. The results indicated that the Rh(acac)P, complex was the active catalyst, which led to a good reaction yield and a high selectivity of the n/iso ratio. Important information characterising the course of the reaction may be obtained from the data presented in Table 1. Increasing the pressure causes a considerable lowering of the n/iso ratio, e.g. at the same reagent concentrations the pressure enhancement from 1 to 11 atm results in a drop of the n/iso ratio from 20.5 to 3.9 (or from 83 to 4.6). Pressure increase is accompanied by an increase in the total yield of aldehydes at the expense of isomerisation products. The second trend applies to the influence of phosphite concentration on the composition of the reaction products. With increasing phosphite concentration, the n/iso ratio first grows and then declines (at 1 atm) or becomes stable (at higher pressure). It should be emphasized that the optimal reaction course (high efficiency and selectivity) requires only a small phosphite excess towards a complex. In contrast to the phosphine catalysts, which require even a lOOfold excess of phosphine [4, 51, our catalyst operates with best efficiency at -two-fold phosphite excess. This fact we have already observed in reactions carried out at enhanced pressure and temperature [ 21. A change in the phosphite concentration results in a drastic change in the hydroformylation rate. To estimate the reaction rate, we have measured the volume of (Hz + CO) mixture consumed by the reacting system. The time dependence of the volume of (H, + CO) mixture consumed in several experiments is presented in Fig. 1, which shows that an increase in phosphite concentration is responsible for the decline in the gas consumption rate; and, simultaneously, the decrease in the hydroformylation rate. In our opinion, this phenomenon is caused mainly by the difficulty in coordinating olefin to the rhodium ion in the complex in the presence of excess free phosphite ligand. In our most recent studies [6,7] we have not noticed any
215 TABLE 1 Hydroformylation P (atm) 1
of hex-1-ene with Rh(acac)[P(OPh)slz
F’(OPh)31 [Rhl
as catalyst at [H2]:[CO]
Composition of reaction mixture n-aldehyde
iso-aldehyde
hex-2ene
hex-l ene
-
1.3 2.0 2.6 4.0 4.9 6.0
63.6 61.0 32.5 33.6 32.3 15.4
6.4 3.0 0.5 0.4 1.7 0.6
30.0 27.0 59.0 57.0 35.0 30.0
1.3 2.0 4.4 6.1
17.9 34.3 34.9 36.6
2.1 1.7 1.1 1.4
80.0 46.0 14.0 31.0
8
1.3 2.1 2.6 4.7
46.6 50.9 32.9 52.5
19.4 9.1 4.1 7.5
11
1.3 2.0 4.0
60.7 53.3 73.1
25.3 13.7 15.9
4.0 4.0
[Ha]:[CO] [HJ:[CO]
2
11 11
13.0 8.0 9.0 31.0 50.0 -
= la n/is0 ratio 10.0 20.5 65.0 83.0 19.4 25.4
18.0 50.0 31.0
8.4 20.0 32.0 26.0
6.0 14.0 37.0 18.0
44.0 26.0 26.0 22.0
2.3 5.6 8.1 7.0
14.0 33.0 7.0
-
2.4 3.9 4.6
4
= 3:l = 1:3
aReaction carried out in benzene (0.8 ml) at 40 “C; [hex-l-ene] [Rh] = 2.5 x lo-’ M, reaction time 5 h.
6.4 3.7 = 3.2
x
Fig. 1. Volume of (CO + Ha) consumed in hex-1-ene hydroformylation Rh(acac)Pz+P; [P]:[Rh] = X 1.3;+ 2.6;04.9;@6.0.
10e3 M (0.4 ml);
reaction with
effect of phosphite concentration on the efficiency of reaction of the rhodium complex with Hz and CO. ‘H and 31P NMR spectra of the system containing Rh(acac)P, + P + H, + CO led us to conclude [6] that in a solution there are present two
216
hydride complexes: HRhP4 and HRh(CO)Ps. The concentration ratio of these two compounds could easily be modified, depending on the amount of CO and H2 in the system. NMR measurements made for the same system, under normal pressure in the presence of hex-1-ene, allowed us to designate HRh(CO)P3 as the active form of hydroformylation catalyst [6]. In this paper we also report structural studies of a catalyst in the actual hydroformylation reaction carried out using IR spectroscopy, previously found to be most useful in such studies [7]. In the first experiment, the reaction was carried out at 1 atm and the IR spectra were periodically recorded in the V(CO)range. After 10 min, two bands had already appeared, at 2010 and 2050 cm-l, the former the more intense. The intensity of the bands increased with time, but their height ratio remained constant. This spectrum was characteristic for the Rh(acac)(CO),P complex [7]. After 80 min the intensity of the band at 2010 cm-’ decreased, with an increase of that at 2050 cm-‘. After -150 min, the intense band at 2050 cm-’ and only traces of the band at 2010 cm-’ were observed (Fig. 2). Such a spectrum points to the predominance of the HRh(CO)Ps hydride complex in solution. Previously, we had tentatively assigned this spectrum to the HRh(acac)(CO)P, complex [7]. Our recent research [6], however, revealed that this compound contained no acetylacetonate ligand. The rate of formation of the active hydride complex is pressure dependent - enhancement of the pressure slows the rate of formation of HRh(CO)P,. At 3 atm, after 45 min, HRh(CO)P3 is the main product in solution, while at 11 atm, after the same time, the carbonyl form Rh(acac)(C0)2P is predominant. After 2 h at 3 atm only HRh(CO)P, is present, while at 11 atm Rh(acac)(CO),P still predominates (Fig. 3). After 3 h at 11 atm, HRh(CO)P, is the only form present in solution. The results of our measurements reported here allow us to conclude that an enhancement in pressure, at a H,:CO = 1 ratio, will increase the concentration of CO-containing complexes and simultaneously increase the existence of trace amounts of HRhP4. HRhP4 reacts immediately with CO to produce HRh(CO)P, [6]. Since HRhP, is the hex-1-ene isomerisation catalyst [6], the decreasing contribution of hex-2ene in the products with increasing pressure is obvious. We have also analyzed the products of the reaction carried out at a gas ratio different than H,:CO = 1 (Table 1) and we have interpreted their IR spectra. An increase in the partial hydrogen pressure of a mixture of gases results in an increase in the amount of n-aldehyde, while an increase in CO pressure produces the reverse effect. The IR spectrum of a complex after reaction carried out at H2:C0 = 3 is characteristic for HRh(CO)P3, while in the case of H,:CO = 1:3, the presence of the band at 2010 cm-’ obviously points to a shift of the equilibrium towards the carbonyl complexes. Different n/iso values could be explained in this case not only by a change in the catalyst structure, but also by the influence of HZ and CO on the subsequent reaction stages. A decrease of the n/iso ratio at higher partial CO pressure could be due to the facilitation of CO insertion into the complex with a branched alkyl
217
1800
2000
2200
cm-’
800
2c
.300
2000
cm’
p=3atm
p-vat
/I ::”
J J II
Fig. 2. IR spectrum in the range 2200 - 1600 cm -I for the hydroformylation with Rh(acac)Pz + P at P= 1 atm; [P]:[Rh] = 2.0. Fig. 3. IR spectrum in the range 2200 - 1800 cm-’ in hex-l-ene Rh(acac)Pz + P; [P]:[Rh] = 4.0; (1) 45 min; (2) 120 min.
of hex-l-me
hydroformylation
with
coordinated to the metal center, which then results in an increase in the amount of iso-aldehyde. Increasing the partial Hz pressure was found to limit the isomerisation of the coordinated olefin and to shift the equilibrium towards the complex with linear alkyl. Similar suggestions are reported also by other authors [S] . For a comparison of catalytic activity of the two hydride complexes HRhP4 and HRh(CO)Ps formed in situ in the system used, we have examined the reaction Rh(acac)P, + P + H2 + hex-lene at the same concentrations as those used in the hydroformylation reaction. Experiments were carried out under hydrogen atmosphere; under such conditions the only reaction was that of isomerisation of hex-l-ene to hex-2-ene. The changes in hex-2ene concentration with time for several selected reactions are shown in Fig. 4. Evident dependence of the hex-2-ene formation rate on the concentration of the phosphite added was observed - the higher the concentration, the slower the reaction. As in the case of hydroformylation, that fact could be explained in terms of the difficult coordination of olefin to catalyst. A comparison of the amounts of hex-2ene obtained in reactions carried out under H, + CO and H, atmosphere revealed the inhibiting effect
218
ttme/h
Fig. 4. Mel% of hex-2-ene in the hex-l -ene isomerisation with Rh(acac)Pz + P; [P]:[Rh] 0 1.3; x 3.0; + 4.0;. 4.8; @ 6.6.
=
of CO on isomerisation reactions. For example, for reaction at a concentration ratio [P] : [ Rh] = 1:3 without CO, after only 4 h the 100% conversion of hex-1-ene to hex-2-ene was observed, while in the presence of CO the converTABLE 2 Hydroformylation
of propylene with Rh(acac)[P(OPh)a]z
Partial pressure of substrates (atm)
]P(CPh)al
[Rhl 1
as catalysta
Propylene conversionC (%I
(n + iso) aldehydesd (%I
n/is0
[Hz1
[CO1
browlene
1.5
1.5
2.0
1.0 1.9 4.0
20 23 31
1 15 27
2.6 5.2 4.7
2.0
2.0
2.0
1.8 2.7 2.7 4.2
41 32 28 42
17 27 17 28
2.7 4.4 2.2b 4.3
3.0
3.0
2.0
1.0 1.7 4.4
18 52 70
3 60 43
2.0 2.5 2.5
4.5 4.0 1.5
1.5 2.0 4.5
2.0 2.0 2.0
1.9 1.8 1.8
95 71 29
10 20 20
10.0 6.5 2.1
4.0
4.0
2.0
0.8 2.0 6.5
17 70 73
4 61 37
1.9 2.5 2.1
aReaction carried out in benzene 0.8 ml, 40 “C, [ Rh] = 2.5 X 10e5 M. Catalyst, phosphite and benzene were placed into the autoclave filled with propylene, Hz and CC to proper pressure; reaction time 7 h. bCarbon monoxide was added first, then hydrogen. CEstimated from the pressure decrease. dCalculated from the ‘H NMR spectra using dioxane as standard.
219
sion reached only 30% of hex-2-ene after 5 h. This supported our suggestion that HRhP4 is the only form which catalyzes isomerisation in our system. In the presence of. CO, HRhP4 was converted into HRh(CO)P,, which limited isomerisation . Hydroformylation of propylene The catalytic system Rh(acac)P, + P was also used for propylene hydroformylation at 5 - 10 atm pressure and 40 “C. The composition of the aldehydes obtained is given in Table 2. Our results suggested that the general tendencies observed for the hydroformylation of hex-l-ene apply also to propylene. In both cases, the system reached its maximum activity (high yield of aldehydes) at only a small excess of triphenylphosphite. With pressure increase, the total amount of aldehydes increased and the n/iso ratio declined. Selectivity (n/iso) improved with increasing Hz partial pressure, but the amount of hydrogenation products simultaneously increased. Hydroformylation reactions of hex-1-ene and of propylene are very much alike, but the essential difference in the n/iso values obtained in both cases should not be neglected, In the case of propylene, the selectivity not only is much lower, but also depends very little on reaction conditions. References 1 2 3 4 5 6
D. Pieta, A. M. Trzeciak and J. J. Ziblkowski, J. Mol. Catal., 18 (1983) 193. H. Janecko, A. M. Trzeciak and J. J. Ziblkowski, J. Mol. Catal., 26 (1984) 355. A. M. Trzeciak and J. J. ZWkowski, Inorg. Chim. Acta, 64 (1982) L267. M. Matsumoto and M. Tamura, J. Mol. Catal., 16 (1982) 209. 0. R. Hughesand J. D. Unruh, J. Mol. Catai., 12 (1981) 71. A. M. Trzeciak, J. J. Zitikowski, S. Aygen and R. van Eldik, J. Mol. Catal, 34 (1986) 337. 7 A. M. Trzeciak and J. J. ZWkowski, J. Mol. Catal., 19 (1983) 41. 8 J. D. Unruh and J. R. Christenson, J. Mol. Catal., 14 (1982) 19.
Catalysis, 34 (1986)
213 - 219
213
LOW PRESSURE, HIGHLY ACTIVE RHODIUM CATALYST FOR THE HOMOGENEOUS HYDROFORMYLATION OF OLEFINS A. M. TRZECIAK Institute
and J. J. ZI6LKOWSKI
of Chemistry,
(Received March 1,1985;
University
of Wrockaw, 50-383
Wrodhw
(Poland)
accepted June 21,1985)
Summary Hex-1-ene hydroformylation was examined at pressures of 1 - 11 atm and 40 “C, using Rh(acac)[P(OPh),], + P(OPh)s as catalyst. The highest efficiency of aldehydes was achieved employing a small P(OPhs), excess [P(OPh),]:[Rh] = 2:l. For reactions carried out at 1 atm, very high n/iso ratios i.e. lo-80 were obtained. Pressure increase caused a systematic drop of the n/iso ratio to ca. 5 at 11 atm. Simultaneously with hydroformylation, isomerisation of hex-lene to hex-2-ene occurs, but the contribution of the latter declines with increasing pressure. IR examination of the reaction mixture revealed that HRh(CO)[P(OPh)s]s was the active form of the catalyst. The same catalytic system was applied in propylene hydroformylation at 5 - 10 atm pressure and 40 “C. In such conditions the yield of aldehydes was 10 - 7096, with a n/iso selectivity of 2 - 10.
Introduction Rhodium(I) complexes containing a single ,&diketonate ligand of the type Rh@-diket.)LILz (where Li, LZ = CO, PPhs) have been recognized for many years as very convenient precursors for homogeneous catalysts of such reactions as hydrogenation, isomerisation and hydroformylation of olefins. In our recent papers on the catalytic reactivity of Rh(acac)[P(OPh),],, the hydrogenation of arenes [l] and hydroformylation [ 21 of olefins have been reported. This paper presents new results on the homogeneous hydroformylation of hex-1-ene and propylene. Experimental Rh(acac)Bis(triphenylphosphite)(acetylacetonato)rhodium(I), was obtained according to the method described earlier [3] P(OPhM,, (P(OPh), = P). IR spectra in benzene solution were recorded on a Specord 0304-5102/86/$3.50
0 Elsevier Sequoia/Printed in The Netherlands
214
75 IR instrument. The hex-l-ene hydroformylation products were analyzed by GLC and NMR methods (in Table 1 average results of both methods are given). GLC analysis: n- and iso-aldehydes were determined on a Chrom 4 instrument with cyclohexene as internal standard. NMR analysis: total amount of aldehydes, as well as amounts of hex-l-ene and hex-2-ene, were determined from the appropriate peak area on the ‘H NMR spectra. Dioxane was used as an internal standard. ‘H NMR spectra were recorded on a Tesla 80 MHz spectrometer. Propylene hydroformylation products were determined from ‘H NMR.
Results and discussion Hydroformylation of hex-l-ene Hex-1-ene hydroformylation was carried out under mild conditions, at 1 - 11 atm pressure and 40 “C. The composition of the reaction products is shown in Table 1. The results indicated that the Rh(acac)P, complex was the active catalyst, which led to a good reaction yield and a high selectivity of the n/iso ratio. Important information characterising the course of the reaction may be obtained from the data presented in Table 1. Increasing the pressure causes a considerable lowering of the n/iso ratio, e.g. at the same reagent concentrations the pressure enhancement from 1 to 11 atm results in a drop of the n/iso ratio from 20.5 to 3.9 (or from 83 to 4.6). Pressure increase is accompanied by an increase in the total yield of aldehydes at the expense of isomerisation products. The second trend applies to the influence of phosphite concentration on the composition of the reaction products. With increasing phosphite concentration, the n/iso ratio first grows and then declines (at 1 atm) or becomes stable (at higher pressure). It should be emphasized that the optimal reaction course (high efficiency and selectivity) requires only a small phosphite excess towards a complex. In contrast to the phosphine catalysts, which require even a lOOfold excess of phosphine [4, 51, our catalyst operates with best efficiency at -two-fold phosphite excess. This fact we have already observed in reactions carried out at enhanced pressure and temperature [ 21. A change in the phosphite concentration results in a drastic change in the hydroformylation rate. To estimate the reaction rate, we have measured the volume of (Hz + CO) mixture consumed by the reacting system. The time dependence of the volume of (H, + CO) mixture consumed in several experiments is presented in Fig. 1, which shows that an increase in phosphite concentration is responsible for the decline in the gas consumption rate; and, simultaneously, the decrease in the hydroformylation rate. In our opinion, this phenomenon is caused mainly by the difficulty in coordinating olefin to the rhodium ion in the complex in the presence of excess free phosphite ligand. In our most recent studies [6,7] we have not noticed any
215 TABLE 1 Hydroformylation P (atm) 1
of hex-1-ene with Rh(acac)[P(OPh)slz
F’(OPh)31 [Rhl
as catalyst at [H2]:[CO]
Composition of reaction mixture n-aldehyde
iso-aldehyde
hex-2ene
hex-l ene
-
1.3 2.0 2.6 4.0 4.9 6.0
63.6 61.0 32.5 33.6 32.3 15.4
6.4 3.0 0.5 0.4 1.7 0.6
30.0 27.0 59.0 57.0 35.0 30.0
1.3 2.0 4.4 6.1
17.9 34.3 34.9 36.6
2.1 1.7 1.1 1.4
80.0 46.0 14.0 31.0
8
1.3 2.1 2.6 4.7
46.6 50.9 32.9 52.5
19.4 9.1 4.1 7.5
11
1.3 2.0 4.0
60.7 53.3 73.1
25.3 13.7 15.9
4.0 4.0
[Ha]:[CO] [HJ:[CO]
2
11 11
13.0 8.0 9.0 31.0 50.0 -
= la n/is0 ratio 10.0 20.5 65.0 83.0 19.4 25.4
18.0 50.0 31.0
8.4 20.0 32.0 26.0
6.0 14.0 37.0 18.0
44.0 26.0 26.0 22.0
2.3 5.6 8.1 7.0
14.0 33.0 7.0
-
2.4 3.9 4.6
4
= 3:l = 1:3
aReaction carried out in benzene (0.8 ml) at 40 “C; [hex-l-ene] [Rh] = 2.5 x lo-’ M, reaction time 5 h.
6.4 3.7 = 3.2
x
Fig. 1. Volume of (CO + Ha) consumed in hex-1-ene hydroformylation Rh(acac)Pz+P; [P]:[Rh] = X 1.3;+ 2.6;04.9;@6.0.
10e3 M (0.4 ml);
reaction with
effect of phosphite concentration on the efficiency of reaction of the rhodium complex with Hz and CO. ‘H and 31P NMR spectra of the system containing Rh(acac)P, + P + H, + CO led us to conclude [6] that in a solution there are present two
216
hydride complexes: HRhP4 and HRh(CO)Ps. The concentration ratio of these two compounds could easily be modified, depending on the amount of CO and H2 in the system. NMR measurements made for the same system, under normal pressure in the presence of hex-1-ene, allowed us to designate HRh(CO)P3 as the active form of hydroformylation catalyst [6]. In this paper we also report structural studies of a catalyst in the actual hydroformylation reaction carried out using IR spectroscopy, previously found to be most useful in such studies [7]. In the first experiment, the reaction was carried out at 1 atm and the IR spectra were periodically recorded in the V(CO)range. After 10 min, two bands had already appeared, at 2010 and 2050 cm-l, the former the more intense. The intensity of the bands increased with time, but their height ratio remained constant. This spectrum was characteristic for the Rh(acac)(CO),P complex [7]. After 80 min the intensity of the band at 2010 cm-’ decreased, with an increase of that at 2050 cm-‘. After -150 min, the intense band at 2050 cm-’ and only traces of the band at 2010 cm-’ were observed (Fig. 2). Such a spectrum points to the predominance of the HRh(CO)Ps hydride complex in solution. Previously, we had tentatively assigned this spectrum to the HRh(acac)(CO)P, complex [7]. Our recent research [6], however, revealed that this compound contained no acetylacetonate ligand. The rate of formation of the active hydride complex is pressure dependent - enhancement of the pressure slows the rate of formation of HRh(CO)P,. At 3 atm, after 45 min, HRh(CO)P3 is the main product in solution, while at 11 atm, after the same time, the carbonyl form Rh(acac)(C0)2P is predominant. After 2 h at 3 atm only HRh(CO)P, is present, while at 11 atm Rh(acac)(CO),P still predominates (Fig. 3). After 3 h at 11 atm, HRh(CO)P, is the only form present in solution. The results of our measurements reported here allow us to conclude that an enhancement in pressure, at a H,:CO = 1 ratio, will increase the concentration of CO-containing complexes and simultaneously increase the existence of trace amounts of HRhP4. HRhP4 reacts immediately with CO to produce HRh(CO)P, [6]. Since HRhP, is the hex-1-ene isomerisation catalyst [6], the decreasing contribution of hex-2ene in the products with increasing pressure is obvious. We have also analyzed the products of the reaction carried out at a gas ratio different than H,:CO = 1 (Table 1) and we have interpreted their IR spectra. An increase in the partial hydrogen pressure of a mixture of gases results in an increase in the amount of n-aldehyde, while an increase in CO pressure produces the reverse effect. The IR spectrum of a complex after reaction carried out at H2:C0 = 3 is characteristic for HRh(CO)P3, while in the case of H,:CO = 1:3, the presence of the band at 2010 cm-’ obviously points to a shift of the equilibrium towards the carbonyl complexes. Different n/iso values could be explained in this case not only by a change in the catalyst structure, but also by the influence of HZ and CO on the subsequent reaction stages. A decrease of the n/iso ratio at higher partial CO pressure could be due to the facilitation of CO insertion into the complex with a branched alkyl
217
1800
2000
2200
cm-’
800
2c
.300
2000
cm’
p=3atm
p-vat
/I ::”
J J II
Fig. 2. IR spectrum in the range 2200 - 1600 cm -I for the hydroformylation with Rh(acac)Pz + P at P= 1 atm; [P]:[Rh] = 2.0. Fig. 3. IR spectrum in the range 2200 - 1800 cm-’ in hex-l-ene Rh(acac)Pz + P; [P]:[Rh] = 4.0; (1) 45 min; (2) 120 min.
of hex-l-me
hydroformylation
with
coordinated to the metal center, which then results in an increase in the amount of iso-aldehyde. Increasing the partial Hz pressure was found to limit the isomerisation of the coordinated olefin and to shift the equilibrium towards the complex with linear alkyl. Similar suggestions are reported also by other authors [S] . For a comparison of catalytic activity of the two hydride complexes HRhP4 and HRh(CO)Ps formed in situ in the system used, we have examined the reaction Rh(acac)P, + P + H2 + hex-lene at the same concentrations as those used in the hydroformylation reaction. Experiments were carried out under hydrogen atmosphere; under such conditions the only reaction was that of isomerisation of hex-l-ene to hex-2-ene. The changes in hex-2ene concentration with time for several selected reactions are shown in Fig. 4. Evident dependence of the hex-2-ene formation rate on the concentration of the phosphite added was observed - the higher the concentration, the slower the reaction. As in the case of hydroformylation, that fact could be explained in terms of the difficult coordination of olefin to catalyst. A comparison of the amounts of hex-2ene obtained in reactions carried out under H, + CO and H, atmosphere revealed the inhibiting effect
218
ttme/h
Fig. 4. Mel% of hex-2-ene in the hex-l -ene isomerisation with Rh(acac)Pz + P; [P]:[Rh] 0 1.3; x 3.0; + 4.0;. 4.8; @ 6.6.
=
of CO on isomerisation reactions. For example, for reaction at a concentration ratio [P] : [ Rh] = 1:3 without CO, after only 4 h the 100% conversion of hex-1-ene to hex-2-ene was observed, while in the presence of CO the converTABLE 2 Hydroformylation
of propylene with Rh(acac)[P(OPh)a]z
Partial pressure of substrates (atm)
]P(CPh)al
[Rhl 1
as catalysta
Propylene conversionC (%I
(n + iso) aldehydesd (%I
n/is0
[Hz1
[CO1
browlene
1.5
1.5
2.0
1.0 1.9 4.0
20 23 31
1 15 27
2.6 5.2 4.7
2.0
2.0
2.0
1.8 2.7 2.7 4.2
41 32 28 42
17 27 17 28
2.7 4.4 2.2b 4.3
3.0
3.0
2.0
1.0 1.7 4.4
18 52 70
3 60 43
2.0 2.5 2.5
4.5 4.0 1.5
1.5 2.0 4.5
2.0 2.0 2.0
1.9 1.8 1.8
95 71 29
10 20 20
10.0 6.5 2.1
4.0
4.0
2.0
0.8 2.0 6.5
17 70 73
4 61 37
1.9 2.5 2.1
aReaction carried out in benzene 0.8 ml, 40 “C, [ Rh] = 2.5 X 10e5 M. Catalyst, phosphite and benzene were placed into the autoclave filled with propylene, Hz and CC to proper pressure; reaction time 7 h. bCarbon monoxide was added first, then hydrogen. CEstimated from the pressure decrease. dCalculated from the ‘H NMR spectra using dioxane as standard.
219
sion reached only 30% of hex-2-ene after 5 h. This supported our suggestion that HRhP4 is the only form which catalyzes isomerisation in our system. In the presence of. CO, HRhP4 was converted into HRh(CO)P,, which limited isomerisation . Hydroformylation of propylene The catalytic system Rh(acac)P, + P was also used for propylene hydroformylation at 5 - 10 atm pressure and 40 “C. The composition of the aldehydes obtained is given in Table 2. Our results suggested that the general tendencies observed for the hydroformylation of hex-l-ene apply also to propylene. In both cases, the system reached its maximum activity (high yield of aldehydes) at only a small excess of triphenylphosphite. With pressure increase, the total amount of aldehydes increased and the n/iso ratio declined. Selectivity (n/iso) improved with increasing Hz partial pressure, but the amount of hydrogenation products simultaneously increased. Hydroformylation reactions of hex-1-ene and of propylene are very much alike, but the essential difference in the n/iso values obtained in both cases should not be neglected, In the case of propylene, the selectivity not only is much lower, but also depends very little on reaction conditions. References 1 2 3 4 5 6
D. Pieta, A. M. Trzeciak and J. J. Ziblkowski, J. Mol. Catal., 18 (1983) 193. H. Janecko, A. M. Trzeciak and J. J. Ziblkowski, J. Mol. Catal., 26 (1984) 355. A. M. Trzeciak and J. J. ZWkowski, Inorg. Chim. Acta, 64 (1982) L267. M. Matsumoto and M. Tamura, J. Mol. Catal., 16 (1982) 209. 0. R. Hughesand J. D. Unruh, J. Mol. Catai., 12 (1981) 71. A. M. Trzeciak, J. J. Zitikowski, S. Aygen and R. van Eldik, J. Mol. Catal, 34 (1986) 337. 7 A. M. Trzeciak and J. J. ZWkowski, J. Mol. Catal., 19 (1983) 41. 8 J. D. Unruh and J. R. Christenson, J. Mol. Catal., 14 (1982) 19.